Hoping you can help. I do basic css web design for friends charities etc for free(dont think they would pay!). One has asked if I can create a client login area - where registered users can upload and download/share pdf files - no need for modification of pdfs. I really need a recommendation of the best steps to achieve this. My skills are basic - i would like to do this without a backend database if possible using a write protected directory on the server possibly?

I am really struggling with where to begin I have never created a login screen/area before or any of the rest of it for that matter. Help greatly appreciated with best practice and possible examples to help me.